(1) Field of the Invention
The present invention relates to a zirconia porcelain and a method of manufacturing the same. More particularly, the invention relates to a zirconia porcelain consisting essentially of zirconium oxide, yttrium oxide and cerium oxide and a manufacturing method for the zirconia porcelain thereof.
(2) Description of the Prior Art
Zirconia porcelains containing not higher than 5 mol % of only yttrium oxide as a stabilizer have been widely used as high temperature structural materials, cutting tool materials and the like because of its high heat resistance, high strength and high toughness. In the zirconia partially stabilized with yttrium oxide, tetragonal zirconia, which is stable at a high temperature, remains as a metastable phase at low temperatures by controlling the microstructure. Cracking development due to the phase transformation of the monoclinic phase, which is accompanied by a volume expansion, is prevented so as to attain a high strength body. The thus produced zirconia porcelain gradually undergoes transformation from the tetragonal phase to the monoclinic phase over time and because of the application of a thermal stresses, and so on. Thus, the deterioration phenomenon such as shape change and cracking development results in a reduction in the strength.
The metastable tetragonal phase is similar to super cooled state. It is considered that as a time during which the tetragonal phase is exposed to a temperature range of 200.degree. C.-1,000.degree. C. becomes longer, the nuclei of the monoclinic phase are ultimately transformed to the monoclinic phase which is thermodynamically stable. Even under control of the micro structure, when the phase transformation temperature is not less than 200.degree. C., the potential force to cause the transformation is large and the system is still extremely unstable from the standpoint of the thermodynamics because the metastable tetragonal phase is in an extremely super cooled state. Accordingly, there have been strongly demanded zirconia porcelains having a high strength and an excellent thermal stability.